The treatment of various liquids by ultrasonic energy is well known. Ultrasonic energy has proven to be an effective means for homogenizing, dispersing, blending, mixing and reducing particles in one or more liquids, as well as for expediting certain chemical reactions. It is also well known that horn resinators can be employed to concentrate ultrasonic energy. U.S. Pat. Nos. 3,715,104 and 3,825,481 employ horn resonators to couple ultrasonic energy to the treated fluid which may comprise foods, medicaments, cosmetics and the like. Both of these patents teach sonic energy reactors in which the entire tapered horn resinator projects into a chamber through which flows the fluid being treated.
FIG. 1 illustrates an example of a conventional flow cell 10 employing a traditional horn 12, which flow cell 10 includes a housing 14 which defines a flow chamber 16. Housing 14 also includes an inlet 18 and an outlet 20 through which a liquid 22 to be treated is flowed (indicated by arrows). By varying the rate at which liquid 22 is flowed into and out of chamber 16 the level of liquid 22 within chamber 16, as well as the amount of time it spends within flow chamber 16, can be controlled. The end of horn 12 is immersed in liquid 22, and horn 12 is ultrasonically vibrated.
More specifically, an ultrasonic power supply (not shown) converts typical AC electricity to high frequency electrical energy. This electrical energy is transmitted to a piezoelectric transducer within a converter 24, where it is changed to mechanical vibrations in the ultrasonic range. The ultrasonic vibrations are intensified by horn 12 and focused at the tip. The ultrasonic activity of horn 12 imparts the vibration energy to liquid 22, thereby accomplishing the desired result within flow chamber 16. As these processes are well known, more detail is not provided herein.
Liquid 22 flows in front of horn 12 and is circulated through flow chamber 16. Due to the nature of the ultrasonic vibrations and the configuration of horn 12, the ultrasonic energy is generally concentrated at the tip of horn 12. However, ultrasonic energy is not limited to this area, and in fact, some degree of ultrasonic energy can be imparted to liquid 22 in substantially any area where liquid 22 contacts a surface of horn 12. As such, it is desirable to maximize the surface area of horn 12 which is in contact with liquid 22 so as to maximize the dwell time of liquid 22 within the ultrasonic field generated by horn 12 in order to maximize the flow rate of liquid 22 through flow chamber 16. A disadvantage of conventional flow cells, such as flow cell 10 shown in FIG. 1, is that the surface area of horn 12 which is in contact with liquid 22 is relatively small.
Attempts have been made to increase the surface area of the horn which is in contact with the liquid to be treated. FIG. 2 illustrates one such attempt wherein a bell horn 52 is used in conjunction with flow cell 50. Bell horn 52 includes an outer surface 54 and a recess 56 having an inner surface 58. Also, in this design, the inlet 60 is provided higher up along bell horn 52, while the outlet 62 is provided at the bottom of the flow chamber 64 defined by the housing 66. This configuration provides an advantage over the flow cell 10 illustrated in FIG. 1 in that the dwell time of the liquid 68 is increased because the ultrasonic energy of the sidewall of bell horn 52 is exploited in addition to the ultrasonic energy at the tip thereof. This radial ultrasonic energy increases the liquid's exposure path along the outside of bell horn 52.
Thus, liquid 68 is introduced though inlet 60 and along the outer surface 54 of bell horn 52 (indicated by arrows). Ultrasonic exposure begins along the side of bell horn 52 and is most intense at the face thereof just before liquid 68 exits through outlet 62 at the bottom of flow chamber 64. However, it should be noted that the inner surface 58 of bell horn 52 is generally not used for ultrasonic treatment of liquid 68. This is the case because although liquid 68 may initially at least partially fill recess 56 in bell horn 52 such that it contacts a portion of inner wall 58, air or various other gasses which may be dissolved in liquid 68 and caused to escape therefrom or which may be created by the ultrasonic treatment of liquid 68, will generally collect in recess 56, thereby causing the level of liquid 68 initially therein to drop until recess 56 is substantially filled with the air or gasses, and substantially no liquid 68 is located therein (as shown in FIG. 2).
Thus, no ultrasonic treatment of the liquid 68 can occur by operation of inner surface 58 unless flow chamber 64 can be turned on its side or inverted so that the air or gasses do not collect inside recess 56 of bell horn 52. However, in many cases it is not possible or desirable to place flow chamber 64 in these orientations. For example, if a catalyst material for a particular reaction is also present in the chamber or the operating environment does not allow the high voltage converter section to be on its side or up-side-down (e.g., because of safety and/or leakage concerns) it may be necessary that the typical orientation with the bell horn facing downward be maintained.
What is desired, therefore, is a flow cell for the ultrasonic treatment of a liquid passing therethrough which allows for a relatively high flow rate of the liquid therethrough, which provides a relatively high dwell time of the liquid within the ultrasonic field generated by the horn, which provides a relatively large surface in contact with the liquid to be ultrasonically treated, which employs a horn having an outer surface and a recess having an inner surface, both of which surfaces are used to impart ultrasonic energy to the liquid, and which allows the horn to be positioned with its recess facing downward.